How Git Actually Works Under the Hood

Most developers use Git every day and understand almost none of it. That's not an insult, it's just the reality of how most people learn tools. You pick up the commands that get you through the day, you memorize the ones that fix the situations you keep breaking, and you build a working mental model that is almost entirely wrong at the mechanical level. The mental model most people carry looks something like this: Git tracks changes to files. When you commit, it saves a snapshot of what changed. Branches are pointers to different lines of work. That's roughly correct at a surface level, but it skips over the actual machinery in a way that leaves you confused every time something unexpected happens. Why does rebasing rewrite history? Why are commits immutable? Why does detached HEAD state exist? Why can you lose work in ways that feel impossible if Git is just tracking changes? The answers are all in the object model, and the object model is surprisingly simple once you sit with it. Git is a content-addressable filesystem Before any of the version control concepts, Git is a key-value store. You put content in, you get a hash back. You use that hash later to retrieve the content. That's the entire foundation, and everything else is built on top of it. The hash Git uses is SHA-1, producing a 40-character hexadecimal string. When you run git hash-object on a file, Git takes the content, prepends a small header describing the object type and size, and runs SHA-1 over the whole thing. The resulting hash is both the key and the identity of that content. Two files with identical content will always produce the same hash. A file whose content changes even slightly will produce a completely different hash. This is the first thing that breaks people's mental models. In most storage systems, identity is location: a file is "that file" because it lives at that path. In Git's object store, identity is content. The path a file lives at is separate metadata, not the file's identity